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Molecular Genetics

Molecular Genetics. DNA RNA Gene Expression. DNA and RNA. DNA deoxyribonucleic acid Deoxribose sugar 2 strands held together with H bonds ATGC are the nitrogen bases Double helix Found only inside the nucleus RNA ribonucleic acid Ribose sugar and AUGC nitrogen bases 1 strand

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Molecular Genetics

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  1. Molecular Genetics DNA RNA Gene Expression

  2. DNA and RNA • DNA deoxyribonucleic acid • Deoxribose sugar • 2 strands held together with H bonds • ATGC are the nitrogen bases • Double helix • Found only inside the nucleus • RNA ribonucleic acid • Ribose sugar and AUGC nitrogen bases • 1 strand • 4 types, mRNA, tRNA, rRNA, and snRNA

  3. Compare RNA and DNA

  4. Replication • DNA replication • Replication is semi-conservative • Occurs during interphase when each chromosome makes an exact copy (sister chromatid)

  5. DNA Replication cont’d • Involves several enzymes • Helicase- unwinds the helix • DNA polymerase- adds new nucleotide units to the parent strand of DNA • Ligase- connects the new strand and zips the molecule together. http://www.dnai.org/a/index.html

  6. Problem with replication? • At the end of each DNA molecule is a section of noncoding nucleotides called a telomere

  7. Telomere cont’d • Each time a cell divides and replicates its DNA a small part of the telomere is lost • This loss of telomere limits the number of times a cell can divide. • This erosion of the telomere during cell division is linked to the aging process and cancer • The enzyme telomerase is inactive in somatic cells but is active in cancer tumors. Can you identify the function of telomerase????

  8. Chromatin • In each cell DNA molecules are organized and wrapped around small proteins called histones. • The density of this wrapping is directly related to the expression of the genes found on the chromosome. • Dense wrapped – no gene expression • Lose wrapped – open to gene expression

  9. Gene experssion • Genes are located on the chromosome at a particular loci • When the gene is signaled to be expressed a series of enzymes go to work • helicase, RNA polymerase, ligase • Transcription occurs when the template strand of DNA is exposed and mRNA is made http://www.dnai.org/a/index.html

  10. Transcription • Process of making a mRNA molecule from the DNA template. • DNA - A T A G C A T A C T A G G • mRNA- U A U C G U A U G A U C C Transcription occurs with in the nucleus, after the mRNA is made however it goes through a series of modifications call RNA processing. This process allows for one gene to express multiple proteins, and is considered to be an element of the evolution process.

  11. Protein Synthesis • mRNA leaves the nucleus of the cell and moves into the rough ER. • A ribosome attaches to the mRNA and starts to Translate the sequence of nucleotides into a protein. • Translation involves several players: rRNA, mRNA, tRNA, amino acids, and enzymes http://www.dnai.org/a/index.html

  12. Translation • Translation occurs at the ribosome, and reads the mRNA 3 nucleotides at a time • 3 nucleotides make up a codon, which codes for 1 amino acid. • There are 64 different codons and only 20 amino acids. So there is repetition in the code • AUG is the universal start codon and codes for the amino acid Met. • There are 3 stop codons that terminate translation: UGA, UAA, UAG

  13. Translation cont’d • Once the codon enters the ribosome the complementary, anticodon, of the tRNA attaches to the mRNA. • The tRNA carries with it a specific amino acid, the amino acids are then bonded to each other as each sequential codon is read by the ribosome http://www.dnai.org/a/index.html The end result is a very specific amino acid chain called a polypeptide or protein.

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